WO2006013546A2 - Process for the preparation of pure galantamine - Google Patents

Process for the preparation of pure galantamine Download PDF

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Publication number
WO2006013546A2
WO2006013546A2 PCT/IB2005/052553 IB2005052553W WO2006013546A2 WO 2006013546 A2 WO2006013546 A2 WO 2006013546A2 IB 2005052553 W IB2005052553 W IB 2005052553W WO 2006013546 A2 WO2006013546 A2 WO 2006013546A2
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WIPO (PCT)
Prior art keywords
galantamine
formula
pharmaceutically acceptable
acceptable salt
hydrobromide
Prior art date
Application number
PCT/IB2005/052553
Other languages
French (fr)
Other versions
WO2006013546A3 (en
Inventor
Saswata Lahiri
Mohan Prasad
Nitin Maheshwari
Yatendra Kumar
Original Assignee
Ranbaxy Laboratories Limited
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Publication of WO2006013546A2 publication Critical patent/WO2006013546A2/en
Publication of WO2006013546A3 publication Critical patent/WO2006013546A3/en

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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D491/00—Heterocyclic compounds containing in the condensed ring system both one or more rings having oxygen atoms as the only ring hetero atoms and one or more rings having nitrogen atoms as the only ring hetero atoms, not provided for by groups C07D451/00 - C07D459/00, C07D463/00, C07D477/00 or C07D489/00
    • C07D491/02—Heterocyclic compounds containing in the condensed ring system both one or more rings having oxygen atoms as the only ring hetero atoms and one or more rings having nitrogen atoms as the only ring hetero atoms, not provided for by groups C07D451/00 - C07D459/00, C07D463/00, C07D477/00 or C07D489/00 in which the condensed system contains two hetero rings
    • C07D491/10—Spiro-condensed systems
    • C07D491/107—Spiro-condensed systems with only one oxygen atom as ring hetero atom in the oxygen-containing ring
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
    • A61P25/00—Drugs for disorders of the nervous system
    • A61P25/18—Antipsychotics, i.e. neuroleptics; Drugs for mania or schizophrenia
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
    • A61P25/00—Drugs for disorders of the nervous system
    • A61P25/28—Drugs for disorders of the nervous system for treating neurodegenerative disorders of the central nervous system, e.g. nootropic agents, cognition enhancers, drugs for treating Alzheimer's disease or other forms of dementia

Definitions

  • the field of the invention relates to processes for the preparation of pure galantamine or pharmaceutically acceptable salts thereof. More particularly, it relates to the preparation of pure galantamine hydrobromide.
  • the invention also relates to pharmaceutical compositions that include the pure galantamine or pharmaceutically acceptable salts thereof and use of said compositions for treating Alzheimer's disease, dementia, mania, fatigue syndrome, and schizophrenia.
  • (-)-Galantamine of Formula I is a tertiary amaryllidaceae alkaloid of high pharma ⁇ cological activity. Chemically, galantamine is
  • Galantamine is indicated for the treatment of mild to moderate dementia of the Alzheimer's type.
  • Galantamine is commercially available in the form of galantamine hydrobromide and is useful in treatment of Alzheimer's disease, dementia, mania, fatigue syndrome, schizophrenia and for inhibiting acetyl cholinesterase activity and reported in literature for example, in U.S. Patent Nos. 4,663,318; 5,312,817; 5,336,675; 5,633,238 and 6,319,919.
  • Galantamine can be isolated from daffodils ⁇ Narcissus pseudonarcissus L.) by the extraction process which is proved to be quite expensive for pharmaceutical grade material, even when taking into account large scale production efficiencies.
  • the present invention provides a process which does not result in impure galantamine or a pharmaceutically acceptable salt thereof; rather pure galantamine having total impurities less than 1.0% is obtained.
  • the galantamine hydrobromide when made by the process of the present invention is pure and cost efficient thus making the process amenable for commercial scale use.
  • the process includes reducing racemic narwedine of Formula ⁇ ,
  • the reducing agent may be one or more of metal borohydrides wherein the metal may be lithium, aluminium or sodium.
  • the reducing agent may include one or more of Vitride ®, L-selectride®, lithium aluminium hydride, and lithium borohydride.
  • the solvent may be one or more of tetrahydrofuran, 1,4-dioxane, diethyl ether, diisopropyl ether, N-methylpyrrolidine and N,N-dimethylformamide.
  • the process may include further drying of the product obtained.
  • the process may produce the pure galantamine or a pharmaceutically acceptable salt thereof having purity more than 99% when determined by HPLC. In particular, it may produce the pure galantamine or a pharmaceutically acceptable salt thereof having purity more than 99.5% by HPLC.
  • a pure galantamine of Formula I or a pharmaceutically acceptable salt thereof having a purity of more than 99% w/w as determined by HPLC method.
  • the purity of galantamine or a pharma ⁇ ceutically acceptable salt thereof is more than 99.5% w/w as determined by HPLC method.
  • the Form I of galantamine hydrobromide may have the X-ray diffraction pattern of
  • a process for preparing Form I galantamine hydrobromide includes treating galantamine or a pharma ⁇ ceutically acceptable salt thereof with an aqueous alkali to get galantamine base; extracting the galantamine free base in one or more solvents to get a solution containing galantamine free base; concentrating the solution to get a residue; dissolving the residue in a second solvent to get a solution; treating the solution of galantamine base with ethanolic aqueous hydrobromic acid; and isolating the galantamine hydrobromide Form I from the reaction mixture thereof.
  • the process may include further drying of the product obtained.
  • composition that includes a therapeutically effective amount of the Form I of galantamine hy- drobromide; and one or more pharmaceutically acceptable carriers, excipients or diluents.
  • a method of inhibiting acetyl cholinesterase enzyme in a warm-blooded animal comprising providing a pharmaceutical composition to the warm-blooded animal that includes the Form I of galantamine hydrobromide.
  • the compound of Formula I may be further or additionally purified to get the pure galantamine of Formula I, or a pharmaceutically acceptable salt thereof.
  • the reducing agent used in reduction of keto group to hydroxyl func ⁇ tionality and the solvents used in such processes are known to a person of ordinary skills in the art through several literature references.
  • the reducing agent may be one or more of metal borohydrides wherein the metal may be lithium, aluminium or sodium.
  • the reducing agent may include one or more of Vitride ®, L- selectride®, lithium aluminium hydride, and lithium borohydride.
  • the solvent may be one or more of tetrahydrofuran, 1,4-dioxane, diethyl ether, diisopropyl ether, N- methylpyrrolidine and N,N-dimethylformamide.
  • the reduction may be carried out at a temperature of from about -7O 0 C to about 1O 0 C. In particular, it may be carried out at a temperature from about -20 0 C to about 0 0 C.
  • the racemic narwedine of Formula II may be added in lots to a pre-cooled solution of reducing agent in an organic solvent.
  • the temperature of the reaction mass may be raised to about 2O 0 C and the excess reducing agent as well as side products formed can be quenched by addition of ethanol.
  • the resultant mass after filtration gives compound of Formula I as a racemic mixture which can be isolated by converting to a salt such as hydrobromide by treating with hydrobromic acid.
  • the solid salt can be filtered from the reaction mass and dried suitably.
  • the racemic product or its salt obtained can be dissolved in a suitable organic solvent, water or mixtures thereof. If a salt is used then it can be first converted to a free base by treating with a dilute alkali solution.
  • the suitable organic solvent can be one or more of water-miscible or immiscible solvents, including, for example, ethyl acetate, methyl formate, methyl acetate, n-butyl acetate, tetrahydrofuran, methanol, ethanol, isopropanol, n-butanol, dichloromethane, chloroform, carbon tetrachloride, acetone, methyl isobutyl ketone, ethyl methyl ketone, diisobutylketone and acetonirile. Mixtures of all of these solvents are also contemplated.
  • the separated base may be extracted in a water immiscible organic solvent, including, for example, ethyl acetate, methyl formate, methyl acetate, n-butyl acetate, dichloromethane, chloroform and carbon tetrachloride.
  • the organic extract can be con ⁇ centrated and the residue obtained can be re-dissolved in an alcoholic solvent.
  • a suitable alcohol includes one or more of methanol, ethanol, isopropanol, n-butanol and n-propanol.
  • a chiral auxiliary may be added and the resultant mass can be stirred for a sufficient time at lower temperature to induce crystallization of the desired (-)-isomer of galantamine as its salt of chiral auxiliary of Formula III.
  • the pre ⁇ cipitated product can be filtered, washed with cold alcoholic organic solvent and re- crystallized if required to get desired purity.
  • Any chiral auxiliary known to a person skilled in the art can be used.
  • di-4-toluoyl-D-tartaric acid can be used as a chiral auxiliary.
  • the chiral auxiliary salt of Formula III can be converted to a free base of Formula I by treating it with a dilute alkali solution, including, for example, ammonia.
  • a dilute alkali solution including, for example, ammonia.
  • the free base of Formula I can be isolated from the reaction mass by extractive work ⁇ up.
  • the solution of free base can be treated with a pharmaceutically acceptable acid and pharmaceutically acceptable salt of galantamine can be prepared.
  • the salt or the free base can be further or additionally recrystallized to get the pure galantamine of Formula I, or a pharmaceutically acceptable salt thereof.
  • the pure galantamine or a pharmaceutically acceptable salt thereof has a purity of more than 99% w/w as determined by HPLC method. More particularly, the purity of galantamine or a pharmaceutically acceptable salt thereof is more than 99.5% w/w as determined by HPLC method.
  • the pure galantamine or a pharmaceutically acceptable salt thereof has an individual known impurity less than 0.2% w/w with total impurities less than 1% w/w when determined by HPLC method. More particularly, the galantamine has an individual impurity less than 0.1% w/w with total impurities less than 0.5%.
  • the commonly encountered impurities in galantamine are N-desmethylgalantamine of Formula IV, chloromethyl quaternary salt of Formula V, dihydrogalantamine of Formula VI, epigalantamine of Formula VH, narwedine of Formula II, dehydro- galantamine of Formula VIII and bromogalantamine of Formula IX.
  • the pure galantamine or a pharmaceutically acceptable salt thereof has a dehydrogalantamine impurity of Formula VIII less than 0.2% w/w.
  • Dehydro- galantamine is a known impurity but once formed it is very difficult to remove the impurity from the final product. Although this is a metabolite of galantamine, its activity and toxicity is not fully established.
  • the inventors have found a novel polymorphic Form I of galantamine hy- drobromide.
  • the Form I is characterized by its X-ray powder diffraction pattern as shown in Figure 1, infrared spectrum as shown in Figure 2, and differential scanning calorimetry thermogram as shown in Figure 3.
  • the Form I galantamine hydrobromide may be characterized by X-ray diffraction peaks at about 12.66, 13.46, 17.40, 20.56, 23.12, 26.58 and 27.82 ⁇ 0.2 degrees two-theta. It may be further characterized by X-ray diffraction peaks at about 13.16, 24.06, 24.76, 27.28, 28.20, 29.10, 29.40, 30.50, and 31.62 ⁇ 0.2 degrees two- theta.
  • the Form I galantamine hydrobromide may also be characterized by DSC melting exotherm at 28O 0 C with a melting range of about 275° C to 283 0 C.
  • the inventors also have developed a process for the preparation of Form I of galantamine hydrobromide, by treating galantamine or a pharmaceutically acceptable salt thereof with an aqueous alkali to get galantamine base; extracting the galantamine free base in one or more solvents to get a solution containing galantamine free base; concentrating the solution to get a residue; dissolving the residue in a second solvent to get a solution; treating the solution of galantamine base with ethanolic aqueous hy- drobromic acid; and isolating galantamine hydrobromide Form I from the reaction mixture thereof.
  • Galantamine or its pharmaceutically acceptable salt may be taken in water and pH of the reaction mass may be adjusted with an alkali solution to about 8.5 to 9.5. Any alkali can be used including for example, liquor ammonia.
  • the aqueous layer may be extracted with an organic solvent.
  • a suitable solvent includes a solvent in which the galantamine free base is soluble and the solvent is insoluble in water. Some examples of such solvents include chloroform, methylene chloride, ethyl acetate, ethyl formate, methyl formate, methyl acetate, isopropyl acetate, isobutyl acetate and n-butyl acetate.
  • the organic extract may be washed with water to remove traces of inorganic and related organic impurities and the extract may be concentrated. It may be concentrated by distillation at atmospheric pressure or under reduced pressure.
  • the residue of galantamine free base may be dissolved in a second organic solvent including for example, C straight or branched chain alcohols, polar aprotic solvents, C ketones,
  • a suitable alcohol includes one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and t-butanol.
  • polar aprotic solvents include tetrahydrofuran, 1,4-dioxane, N,N-dimethylformamide, dimethylsulphoxide, acetonitrile and N-methylpyrrolidone.
  • ketones include acetone, ethyl methyl ketone, methyl isobutyl ketone, diisobutylketone, methyl t-butyl ketone.
  • a mixture of second organic solvent with water in varying proportions can also be used.
  • the solution obtained may be cooled up to about -15°C to 10 0 C and treated with ethanolic aqueous hydrobromic acid solution to attain a pH of about 2 to 4.
  • the pH may be adjusted to about 2.5 to 3.0. It may be stirred for about 1 to 10 hours; the product obtained may be filtered and washed with a second organic solvent.
  • the product obtained may be further or additionally dried.
  • the product may be further or additionally dried in a tray drier, dried under vacuum and/or in a Fluid Bed Drier.
  • the resulting crystalline galantamine hydrobromide may be formulated into ordinary dosage forms such as, for example, tablets, capsules, pills, solutions, etc. In these cases, the medicaments can be prepared by conventional methods with con ⁇ ventional pharmaceutical excipients.
  • the galantamine hydrobromide can be administered for the treatment of
  • a warm-blooded animal is a member of the animal kingdom possessed of a homeostatic mechanism and includes mammals and birds.
  • the salt is generally administered as part of a pharmaceutical composition with a pharmaceutically acceptable carrier, diluent or excipient and optionally other therapeutic ingredients.
  • the salt may be conventionally formulated into tablets, capsules, suspensions, dispersions, injectables and other pharmaceutical forms. Any suitable route of administration may be employed for example, peroral or parenteral.
  • the filtrate was cooled to 0 to - 5°C and aqueous hydrobromic acid (-48%, 82 ml) was added to adjust the pH to 3.0 to 3.5 at 0 to -5°C. It was stirred for 2 hours at 0 - 5°C.
  • the separated solids were filtered, washed with cold ethanol (300 ml) and air dried at 50 - 55°C till loss on drying was not more than 2.5%.
  • Racemic galantamine hydrobromide (100 gm) was dissolved in water (3200 ml) and the solution was filtered through celite bed. The celite bed was washed with water (300 ml) and washings were combined with the filtrate. The combined aqueous layer was washed with dichloromethane (300 ml) and the organic layer was discarded. To the aqueous layer, dichloromethane (1000 ml) was charged and pH of the aqueous layer was adjusted to 8.9 to 9.1 using aqueous ammonia at 0 - 5°C. The aqueous layer was separated and extracted with dichloromethane (100 ml). The combined organic layers were washed with water (2 x 300 ml) and the organic layer was concentrated under vacuum at 30 - 35°C. The residue was dissolved in methanol (200 ml) and cooled to 5
  • Di-p-toluoyl-D-tartaric acid (105 gm) was separately dissolved in methanol (300 ml) and cooled to 5 - 10 0 C.
  • the solution of tartaric acid was added to the solution of the compound and additional quantity of methanol (250 ml) was used to wash the flask containing solution of tartaric acid. This mixture was stirred for 30 min at 5 - 1O 0 C and for 24 hours at 0 - 2 0 C.
  • the solids were filtered and washed with cold methanol (300 ml).
  • the wet product was crystallized in ethanol (400 ml) by refluxing for 30 minutes followed by stirring at 0 - 2°C for 3 hours, solid was filtered and washed with cold ethanol (100 ml). Crystallization in ethanol was repeated again. Finally, the product was refluxed with methanol (400 ml) for 30 minutes, cooled to 15
  • Ethanolic aqueous hydrobromic acid solution (1:1, 30 ml) was added to adjust pH to 2.5 to 3.0 at 0 to -5 0 C.
  • the resultant mass was stirred for 3 hours at 0 - 5°C, filtered and washed with ethanol (300 ml).
  • the solid product was dried under vacuum at 50 - 55°C till loss on drying is not more than 0.2% to get the pure galantamine hydrobromide having XRD, FTIR and DSC properties as shown in Figures 1, 2 and 3, respectively.
  • Figure 1 is X-ray powder diffraction pattern of Form I of galantamine hy ⁇ drobromide.
  • Figure 2 is an infrared spectrum of Form I of galantamine hydrobromide.
  • Figure 3 is differential scanning calorimetrythermogram of Form I of galantamine hydrobromide.

Abstract

The invention relates to processes for the preparation of pure galantamine or pharmaceutically acceptable salts thereof. More particularly, it relates to the preparation of pure galantamine hy­drobromide. The invention also relates to pharmaceutical compositions that include the pure galantamine or pharmaceutically acceptable salts thereof and use of said compositions for treating Alzheimer's disease, dementia, mania, fatigue syndrome, and schizophrenia.

Description

Description PROCESS FOR THE PREPARATION OF PURE
GALANTAMINE
Technical Field
[1] The field of the invention relates to processes for the preparation of pure galantamine or pharmaceutically acceptable salts thereof. More particularly, it relates to the preparation of pure galantamine hydrobromide. The invention also relates to pharmaceutical compositions that include the pure galantamine or pharmaceutically acceptable salts thereof and use of said compositions for treating Alzheimer's disease, dementia, mania, fatigue syndrome, and schizophrenia.
Background Art
[2] (-)-Galantamine of Formula I is a tertiary amaryllidaceae alkaloid of high pharma¬ cological activity. Chemically, galantamine is
(4aS,6R,8aS)-4a,5,9, 10, 11 , 12-hexahydro-3-methoxy-l l-methyl-6H-benzofuro[3a,3,2e fJ[2]benzazepin-6-ol. Galantamine is indicated for the treatment of mild to moderate dementia of the Alzheimer's type.
Figure imgf000002_0001
[4] FORMULA I
[5] Galantamine is commercially available in the form of galantamine hydrobromide and is useful in treatment of Alzheimer's disease, dementia, mania, fatigue syndrome, schizophrenia and for inhibiting acetyl cholinesterase activity and reported in literature for example, in U.S. Patent Nos. 4,663,318; 5,312,817; 5,336,675; 5,633,238 and 6,319,919.
[6] Galantamine can be isolated from daffodils {Narcissus pseudonarcissus L.) by the extraction process which is proved to be quite expensive for pharmaceutical grade material, even when taking into account large scale production efficiencies.
[7] An alternate source of (-)-galantamine or a pharmaceutically acceptable salt thereof is its chemical synthesis. Some synthetic routes to galantamine have been reported for example, in /. Chem. Soc. 1962, 806; Heterocycles 1977, 8, 277; and Chemical Phar¬ maceutical BuIlWi '8, 26, 3765.
[8] Some processes for the preparation of racemic galantamine have been reported for example, in J. Heterocyclic Chem., 1988, 25, 1809; J. Org. Chem. 1971, 36, 1295; J.
Chemical Society P erUn Trans. 1, 1972, 1513; J. Heterocyclic. Chem. 1973, 10, 35;
Tetrahedron 1989, 45, 3329; and J. American Chemical Society 1988, 110, 314.
However, the racemic galantamine would still need to be resolved. [9] Several processes have been reported for the preparation and/or isolation of galantamine or pharmaceutically acceptable salts thereof for example, in U.S. Patent
Nos. 5,877,172; 6,018,043; 6,043,359; 6,087,495; 6,093,815; 6,184,004; 6,346,618;
6,369,238 and 6,407,229. [10] Notwithstanding these advances, the synthetic approach to (-)-galantamine production in high purity pharmaceutical grade on a commercial scale is still problematic. The formation of impurities and cost effectiveness coupled with low yields is very common. [11] Thus, the present invention provides a process which does not result in impure galantamine or a pharmaceutically acceptable salt thereof; rather pure galantamine having total impurities less than 1.0% is obtained. The galantamine hydrobromide when made by the process of the present invention is pure and cost efficient thus making the process amenable for commercial scale use.
Disclosure
[12] Summary of the Invention
[13] Li one general aspect there is provided a process for the preparation of pure galantamine of Formula I, or a pharmaceutically acceptable salt thereof.
Figure imgf000003_0001
[15] FORMULA I
[16] The process includes reducing racemic narwedine of Formula π,
Figure imgf000003_0002
[18] FORMULA π
[19] with a reducing agent in one or more solvents to get racemic gal; maceutically acceptable salt thereof, treating the racemic galantamine with a chiral auxiliary to get (-)-isomer of Formula III, [20]
Figure imgf000004_0001
[21] FORMULA IH
[22] wherein CHI represent the chiral auxiliary used, and converting the compound of
Formula III to compound of Formula I, or a pharmaceutically acceptable salt thereof.
[23] The reducing agent may be one or more of metal borohydrides wherein the metal may be lithium, aluminium or sodium. The reducing agent may include one or more of Vitride ®, L-selectride®, lithium aluminium hydride, and lithium borohydride. The solvent may be one or more of tetrahydrofuran, 1,4-dioxane, diethyl ether, diisopropyl ether, N-methylpyrrolidine and N,N-dimethylformamide.
[24] The process may include further drying of the product obtained.
[25] The process may produce the pure galantamine or a pharmaceutically acceptable salt thereof having purity more than 99% when determined by HPLC. In particular, it may produce the pure galantamine or a pharmaceutically acceptable salt thereof having purity more than 99.5% by HPLC.
[26] In another general aspect there is provided a pure galantamine of Formula I or a pharmaceutically acceptable salt thereof having a purity of more than 99% w/w as determined by HPLC method. In particular, the purity of galantamine or a pharma¬ ceutically acceptable salt thereof is more than 99.5% w/w as determined by HPLC method.
[27] In another general aspect there is provided Form I of galantamine hydrobromide.
[28] The Form I of galantamine hydrobromide may have the X-ray diffraction pattern of
Figure 1, infrared spectrum of Figure 2, and differential scanning calorimetry thermogram of Figure 3.
[29] In another general aspect there is provided a process for preparing Form I galantamine hydrobromide. The process includes treating galantamine or a pharma¬ ceutically acceptable salt thereof with an aqueous alkali to get galantamine base; extracting the galantamine free base in one or more solvents to get a solution containing galantamine free base; concentrating the solution to get a residue; dissolving the residue in a second solvent to get a solution; treating the solution of galantamine base with ethanolic aqueous hydrobromic acid; and isolating the galantamine hydrobromide Form I from the reaction mixture thereof.
[30] The process may include further drying of the product obtained.
[31] In another general aspect there is provided a pharmaceutical composition that includes a therapeutically effective amount of the Form I of galantamine hy- drobromide; and one or more pharmaceutically acceptable carriers, excipients or diluents.
[32] In another general aspect there is provided a method of inhibiting acetyl cholinesterase enzyme in a warm-blooded animal, the method comprising providing a pharmaceutical composition to the warm-blooded animal that includes the Form I of galantamine hydrobromide.
[33] The details of one or more embodiments of the inventions are set forth in the de¬ scription below. Other features, objects and advantages of the inventions will be apparent from the description and claims.
[34] Detailed Description of the Invention
[35] The inventors have developed a synthetic process for the preparation of pure galantamine, or a pharmaceutically acceptable salt thereof, by reducing racemic narwedine of Formula II,
Figure imgf000005_0001
[37] FORMULA II
[38] with a reducing agent in one or more solvents to get racemic galantamine or a phar¬ maceutically acceptable salt thereof, treating the racemicgalantamine with a chiral auxiliary to get (-)-isomer of Formula III,
Figure imgf000005_0002
[40] FORMULA III
[41] wherein CHI represents the chiral auxiliary used, and converting the compound of
Formula III to compound of Formula I, or a pharmaceutically acceptable salt thereof.
[42] The compound of Formula I may be further or additionally purified to get the pure galantamine of Formula I, or a pharmaceutically acceptable salt thereof.
[43] In general, the reducing agent used in reduction of keto group to hydroxyl func¬ tionality and the solvents used in such processes are known to a person of ordinary skills in the art through several literature references. In particular, the reducing agent may be one or more of metal borohydrides wherein the metal may be lithium, aluminium or sodium. The reducing agent may include one or more of Vitride ®, L- selectride®, lithium aluminium hydride, and lithium borohydride. The solvent may be one or more of tetrahydrofuran, 1,4-dioxane, diethyl ether, diisopropyl ether, N- methylpyrrolidine and N,N-dimethylformamide.
[44] In general, the reduction may be carried out at a temperature of from about -7O0C to about 1O0C. In particular, it may be carried out at a temperature from about -200C to about 00C. The racemic narwedine of Formula II may be added in lots to a pre-cooled solution of reducing agent in an organic solvent.
[45] After completion of reduction, the temperature of the reaction mass may be raised to about 2O0C and the excess reducing agent as well as side products formed can be quenched by addition of ethanol. The resultant mass after filtration gives compound of Formula I as a racemic mixture which can be isolated by converting to a salt such as hydrobromide by treating with hydrobromic acid. The solid salt can be filtered from the reaction mass and dried suitably.
[46] The racemic product or its salt obtained can be dissolved in a suitable organic solvent, water or mixtures thereof. If a salt is used then it can be first converted to a free base by treating with a dilute alkali solution. The suitable organic solvent can be one or more of water-miscible or immiscible solvents, including, for example, ethyl acetate, methyl formate, methyl acetate, n-butyl acetate, tetrahydrofuran, methanol, ethanol, isopropanol, n-butanol, dichloromethane, chloroform, carbon tetrachloride, acetone, methyl isobutyl ketone, ethyl methyl ketone, diisobutylketone and acetonirile. Mixtures of all of these solvents are also contemplated.
[47] The separated base may be extracted in a water immiscible organic solvent, including, for example, ethyl acetate, methyl formate, methyl acetate, n-butyl acetate, dichloromethane, chloroform and carbon tetrachloride. The organic extract can be con¬ centrated and the residue obtained can be re-dissolved in an alcoholic solvent. A suitable alcohol includes one or more of methanol, ethanol, isopropanol, n-butanol and n-propanol. To this solution, a chiral auxiliary may be added and the resultant mass can be stirred for a sufficient time at lower temperature to induce crystallization of the desired (-)-isomer of galantamine as its salt of chiral auxiliary of Formula III. The pre¬ cipitated product can be filtered, washed with cold alcoholic organic solvent and re- crystallized if required to get desired purity. Any chiral auxiliary known to a person skilled in the art can be used. In particular, di-4-toluoyl-D-tartaric acid can be used as a chiral auxiliary.
[48] The chiral auxiliary salt of Formula III can be converted to a free base of Formula I by treating it with a dilute alkali solution, including, for example, ammonia. In general, the free base of Formula I can be isolated from the reaction mass by extractive work¬ up. Alternatively, the solution of free base can be treated with a pharmaceutically acceptable acid and pharmaceutically acceptable salt of galantamine can be prepared.
[49] The salt or the free base can be further or additionally recrystallized to get the pure galantamine of Formula I, or a pharmaceutically acceptable salt thereof.
[50] The pure galantamine or a pharmaceutically acceptable salt thereof has a purity of more than 99% w/w as determined by HPLC method. More particularly, the purity of galantamine or a pharmaceutically acceptable salt thereof is more than 99.5% w/w as determined by HPLC method.
[51] The pure galantamine or a pharmaceutically acceptable salt thereof has an individual known impurity less than 0.2% w/w with total impurities less than 1% w/w when determined by HPLC method. More particularly, the galantamine has an individual impurity less than 0.1% w/w with total impurities less than 0.5%.
[52] The commonly encountered impurities in galantamine are N-desmethylgalantamine of Formula IV, chloromethyl quaternary salt of Formula V, dihydrogalantamine of Formula VI, epigalantamine of Formula VH, narwedine of Formula II, dehydro- galantamine of Formula VIII and bromogalantamine of Formula IX.
Figure imgf000007_0001
[54] FORMULA IV
Figure imgf000007_0002
[56] FORMULA V
Figure imgf000007_0003
[58] FORMULA VI
[59]
Figure imgf000008_0001
[60] FORMULA VII
Figure imgf000008_0002
[62] FORMULA II
Figure imgf000008_0003
[64] FORMULA IX
Figure imgf000008_0004
[66] FORMULA Viπ [67] In one aspect, the pure galantamine or a pharmaceutically acceptable salt thereof has a dehydrogalantamine impurity of Formula VIII less than 0.2% w/w. Dehydro- galantamine is a known impurity but once formed it is very difficult to remove the impurity from the final product. Although this is a metabolite of galantamine, its activity and toxicity is not fully established.
[68] The inventors have found a novel polymorphic Form I of galantamine hy- drobromide. The Form I is characterized by its X-ray powder diffraction pattern as shown in Figure 1, infrared spectrum as shown in Figure 2, and differential scanning calorimetry thermogram as shown in Figure 3.
[69] In general, the Form I galantamine hydrobromide may be characterized by X-ray diffraction peaks at about 12.66, 13.46, 17.40, 20.56, 23.12, 26.58 and 27.82 ± 0.2 degrees two-theta. It may be further characterized by X-ray diffraction peaks at about 13.16, 24.06, 24.76, 27.28, 28.20, 29.10, 29.40, 30.50, and 31.62 ± 0.2 degrees two- theta.
[70] The Form I galantamine hydrobromide may also be characterized by DSC melting exotherm at 28O0C with a melting range of about 275° C to 2830C.
[71] The inventors also have developed a process for the preparation of Form I of galantamine hydrobromide, by treating galantamine or a pharmaceutically acceptable salt thereof with an aqueous alkali to get galantamine base; extracting the galantamine free base in one or more solvents to get a solution containing galantamine free base; concentrating the solution to get a residue; dissolving the residue in a second solvent to get a solution; treating the solution of galantamine base with ethanolic aqueous hy- drobromic acid; and isolating galantamine hydrobromide Form I from the reaction mixture thereof.
[72] Galantamine or its pharmaceutically acceptable salt may be taken in water and pH of the reaction mass may be adjusted with an alkali solution to about 8.5 to 9.5. Any alkali can be used including for example, liquor ammonia. The aqueous layer may be extracted with an organic solvent. A suitable solvent includes a solvent in which the galantamine free base is soluble and the solvent is insoluble in water. Some examples of such solvents include chloroform, methylene chloride, ethyl acetate, ethyl formate, methyl formate, methyl acetate, isopropyl acetate, isobutyl acetate and n-butyl acetate. The organic extract may be washed with water to remove traces of inorganic and related organic impurities and the extract may be concentrated. It may be concentrated by distillation at atmospheric pressure or under reduced pressure. The residue of galantamine free base may be dissolved in a second organic solvent including for example, C straight or branched chain alcohols, polar aprotic solvents, C ketones,
1-4 3-10 water or mixtures thereof. A suitable alcohol includes one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and t-butanol. Examples of polar aprotic solvents include tetrahydrofuran, 1,4-dioxane, N,N-dimethylformamide, dimethylsulphoxide, acetonitrile and N-methylpyrrolidone. Examples of ketones include acetone, ethyl methyl ketone, methyl isobutyl ketone, diisobutylketone, methyl t-butyl ketone. A mixture of second organic solvent with water in varying proportions can also be used.
[73] The solution obtained may be cooled up to about -15°C to 100C and treated with ethanolic aqueous hydrobromic acid solution to attain a pH of about 2 to 4. In particular, the pH may be adjusted to about 2.5 to 3.0. It may be stirred for about 1 to 10 hours; the product obtained may be filtered and washed with a second organic solvent.
[74] The product obtained may be further or additionally dried. For example, the product may be further or additionally dried in a tray drier, dried under vacuum and/or in a Fluid Bed Drier. [75] The resulting crystalline galantamine hydrobromide may be formulated into ordinary dosage forms such as, for example, tablets, capsules, pills, solutions, etc. In these cases, the medicaments can be prepared by conventional methods with con¬ ventional pharmaceutical excipients.
[76] The galantamine hydrobromide can be administered for the treatment of
Alzheimer's disease, dementia, mania, fatigue syndrome, schizophrenia and for inhibiting acetyl cholinesterase activity in a warm-blooded animal.
[77] For the purpose of this disclosure, a warm-blooded animal is a member of the animal kingdom possessed of a homeostatic mechanism and includes mammals and birds.
[78] The salt is generally administered as part of a pharmaceutical composition with a pharmaceutically acceptable carrier, diluent or excipient and optionally other therapeutic ingredients. The salt may be conventionally formulated into tablets, capsules, suspensions, dispersions, injectables and other pharmaceutical forms. Any suitable route of administration may be employed for example, peroral or parenteral.
[79] The present invention is further illustrated by the following examples which are provided merely to be exemplary of the invention and do not limit the scope of the invention. Certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.
[80] Example 1 : Preparation of racemic galantamine hydrobromide
[81] L-Selectride (lithium tri-sec-butylborohydride, 1.0M solution in tetrahydrofuran)
(396.5 g) was charged under nitrogen atmosphere, followed by tetrahydrofuran (100 ml) at 0-50C. This mixture was cooled to -20 to -220C and narwedine (100 g) was charged in lots over a period of about 3 hours at -18 to -20°C. Tetrahydrofuran (25 ml) was used to wash the addition vessel and the reaction mixture was stirred for 30 minutes at -15 to -2O0C. It was heated to 200C and ethanol (400 ml) was added. The reaction mixture was stirred for 30 minutes at 20 - 3O0C, filtered and washed with a mixture of tetrahydrofuran and ethanol (200 ml, 1:1). The filtrate was cooled to 0 to - 5°C and aqueous hydrobromic acid (-48%, 82 ml) was added to adjust the pH to 3.0 to 3.5 at 0 to -5°C. It was stirred for 2 hours at 0 - 5°C. The separated solids were filtered, washed with cold ethanol (300 ml) and air dried at 50 - 55°C till loss on drying was not more than 2.5%.
[82] Yield: 116 g.
[83] Example 2: Preparation of (-) galantamine tartarate
[84] Racemic galantamine hydrobromide (100 gm) was dissolved in water (3200 ml) and the solution was filtered through celite bed. The celite bed was washed with water (300 ml) and washings were combined with the filtrate. The combined aqueous layer was washed with dichloromethane (300 ml) and the organic layer was discarded. To the aqueous layer, dichloromethane (1000 ml) was charged and pH of the aqueous layer was adjusted to 8.9 to 9.1 using aqueous ammonia at 0 - 5°C. The aqueous layer was separated and extracted with dichloromethane (100 ml). The combined organic layers were washed with water (2 x 300 ml) and the organic layer was concentrated under vacuum at 30 - 35°C. The residue was dissolved in methanol (200 ml) and cooled to 5
- 1O0C. Di-p-toluoyl-D-tartaric acid (105 gm) was separately dissolved in methanol (300 ml) and cooled to 5 - 100C. The solution of tartaric acid was added to the solution of the compound and additional quantity of methanol (250 ml) was used to wash the flask containing solution of tartaric acid. This mixture was stirred for 30 min at 5 - 1O0C and for 24 hours at 0 - 20C. The solids were filtered and washed with cold methanol (300 ml). The wet product was crystallized in ethanol (400 ml) by refluxing for 30 minutes followed by stirring at 0 - 2°C for 3 hours, solid was filtered and washed with cold ethanol (100 ml). Crystallization in ethanol was repeated again. Finally, the product was refluxed with methanol (400 ml) for 30 minutes, cooled to 15
- 2O0C, stirred for 3 hours and filtered. It was washed with methanol (100 ml) and air dried at 50 - 550C till loss on drying was not more than 1.0%.
[85] Yield: 57 g.
[86] Example 3: Preparation of crude galantamine hydrobromide
[87] (-) Galantamine tartarate (100 g) was taken in a mixture of dichloromethane (600 ml), water (400 ml) and pH of the mixture was adjusted to 8.9 to 9.1 using aqueous ammonia at 5 - 1O0C. The organic layer was separated and the aqueous layer was extracted with dichloromethane (600 ml). The combined organic layer was washed with water (2 x 300 ml). A mixture of ethanol and -48% aqueous hydrobromic acid (1:1, 1 ml) was added to the organic layer and the mass was concentrated at 30 - 350C under reduced pressure. The free base so obtained was dissolved in a mixture of ethanol (1260 ml) and water (110 ml) and cooled to 0 to -50C. A mixture of ethanol and -48% aqueous hydrobromic acid (1:1, 32 ml) was added at 0 to -5°C to bring pH to 2.5 - 3.0, and stirred for 3 hours at 0 - 5°C. The separated solids were filtered and washed with ethanol (200 ml) to afford crude wet galantamine hydrobromide. This material was used as such for the next step. [88] Yield: 62 g.
[89] Example 4: Preparation of pure galantamine hydrobromide
[90] Crude wet galantamine hydrobromide (62 g) was taken in water (220 ml) and pH of the mixture was adjusted to 8.9 to 9.1 using aqueous ammonia at 10 - 15°C. The free base thus obtained was extracted in ethyl acetate (2 x 750 ml + 375 ml). The combined organic layers were washed with water (2 x 200 ml) and were concentrated at 45 - 5O0C at reduced pressure. The free base was dissolved in a mixture of ethanol (1150 ml) and water (100 ml) at 40 - 5O0C. The solution was filtered through a micron filter and cooled to 0 to -50C. Ethanolic aqueous hydrobromic acid solution (1:1, 30 ml) was added to adjust pH to 2.5 to 3.0 at 0 to -50C. The resultant mass was stirred for 3 hours at 0 - 5°C, filtered and washed with ethanol (300 ml). The solid product was dried under vacuum at 50 - 55°C till loss on drying is not more than 0.2% to get the pure galantamine hydrobromide having XRD, FTIR and DSC properties as shown in Figures 1, 2 and 3, respectively.
[91] Yield: 38 g.
[92] Impurity profile:
[93] a) Any single impurity: Less than 0.2% w/w
[94] b) Total impurities: 0.42% w/w
[95] While the present invention has been described in terms of its specific em¬ bodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.
Description Of Drawings
[96] Figure 1 is X-ray powder diffraction pattern of Form I of galantamine hy¬ drobromide.
[97] Figure 2 is an infrared spectrum of Form I of galantamine hydrobromide.
[98] Figure 3 is differential scanning calorimetrythermogram of Form I of galantamine hydrobromide.

Claims

Claims
[1] A process for the preparation of pure galantamine of Formula I or a pharma¬ ceutically acceptable salt thereof, having purity more than 99% by HPLC,
Figure imgf000013_0001
FORMULA I the process comprising: a) reducing racemic narwedine of Formula II,
Figure imgf000013_0002
FORMULA π with a reducing agent in one or more solvents to get racemic galantamine or a pharmaceutically acceptable salt thereof; b) treating the racemic product of step a) with a chiral auxiliary to get (-)-isomer of Formula HL
Figure imgf000013_0003
FORMULA HI wherein CHI represent the chiral auxiliary used; and c) converting the compound of Formula in to compound of Formula I, or a phar¬ maceutically acceptable salt thereof.
[2] The process of claim 1, wherein the reducing agent comprises one or more of metal borohydrides, wherein the metal is lithium, aluminium or sodium.
[3] The process of claim 1, wherein the reducing agent is L-selectride®. [4] The process of claim 1, wherein the solvent comprises one or more of tetrahydrofuran, 1,
4-dioxane, diethyl ether, diisopropyl ether, N- methylpyrrolidine, and N,N-dimethylformamide.
[5] The process of claim 1, wherein the chiral auxiliary is di-4-toluoyl-D-tartaric acid.
[6] The process of claim 1 , wherein the compound of Formula III is converted to compound of Formula I, by treating it with an alkali.
[7] The process of claim 1 , further comprising purification of compound of Formula
I.
[8] The process of claim 1, further comprising forming the product obtained into a finished dosage form.
[9] A pharmaceutical composition comprising a therapeutically effective amount of pure galantamine of Formula I or a pharmaceutically acceptable salt thereof; and one or more pharmaceutically acceptable carriers, excipients or diluents.
[10] A method of inhibiting acetyl cholinesterase enzyme in a warm-blooded animal, the method comprising providing a dosage form to the warm-blooded animal that includes pure galantamine of Formula I or a pharmaceutically acceptable salt thereof.
[11] Pure galantamine or a pharmaceutically acceptable salt thereof having purity more than 99% when determined by HPLC.
[12] Galantamine or a pharmaceutically acceptable salt thereof having less than 0.2% w/w of dehydrogalantamine of Formula VIE when determined by HPLC.
Figure imgf000014_0001
FORMULA Vm
[13] Form I of galantamine hydrobromide, wherein the galantamine hydrobromide has the X-ray diffraction (XRD) pattern of Figure 1.
[14] The galantamine hydrobromide of claim 13, wherein the galantamine hy¬ drobromide has the X-ray diffraction peaks at about 12.66, 13.46, 17.40, 20.56, 23.12, 26.58 and 27.82 + 0.2 degrees two-theta.
[15] The Form I of galantamine hydrobromide having infrared spectrum of Figure 2.
[16] The Form I of galantamine hydrobromide having differential scanning calorimetry thermogram of Figure 3.
[17] The galantamine hydrobromide of claim 16, wherein the galantamine hy¬ drobromide has a melting exotherm at 28O0C with a melting range of about 2750C to about 2830C.
[18] A process for the preparation of Form I of galantamine hydrobromide, the process comprising: a) treating galantamine or a pharmaceutically acceptable salt thereof with an aqueous alkali to get galantamine base; b) extracting the galantamine free base in one or more solvents to get a solution containing galantamine free base; c) concentrating the solution obtained in step b) to get a residue; d) dissolving the residue obtained in step c) in a second solvent to get a solution; e) treating the solution of galantamine base obtained in step d) with ethanolic aqueous hydrobromic acid; and f) isolating galantamine hydrobromide Form I from the reaction mixture thereof.
[19] The process of claim 18, wherein the alkali is ammonia.
[20] • The process of claim 18, wherein the solvent comprises one or more of chloroform, methylene chloride, ethyl acetate, ethyl formate, methyl formate, methyl acetate, isopropyl acetate, isobutyl acetate and n-butyl acetate.
[21] The process of claim 18, wherein the second solvent comprises one or more of C straight or branched chain alcohol, polar aprotic solvent, C ketone, water, or mixtures thereof. [22] A pharmaceutical composition comprising a therapeutically effective amount of
Form I of galantamine hydrobromide; and one or more pharmaceutically acceptable carriers, excipients or diluents. [23] A method of inhibiting acetyl cholinesterase enzyme in a warm-blooded animal, the method comprising providing a dosage form to the warm-blooded animal that includes Form I of galantamine hydrobromide.
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